In metallurgy a rather great importance is attached to the various funnel like tapping spouts which are used to temporarily delimit the streams of the molten metals during their discharge from one container into another.
The concerned containers are, e.g. refining converters, electric elaboration or treatment furnaces, transfer and alloying ladles, and continuous casting tundishes. The devices used for teeming the liquid metal may be conventional discharge nozzles which are opened and closed with the help of a stopper rod. However, sliding or rotating gate nozzles or valves of the different known types, hereinafter generically called slide gate valves, have now become popular.
The reason is not only an ergonomic one or an economic one due to the fact that it is imperative to be in a position to realize any of the mentioned handlings with the smallest possible danger for the operators and to achieve moreover the best possible yield of the different operations; consideration has also to be given to the metallurgical consequences resulting from the manner in which a nozzle and stopper rod device or a slide gate valve are behaving during their use, that is to say that will be the configuration of the metal stream which is being bundled in the outflow channel of the tapping spout. Unless a very special treatment is requiring a sputtering jet, the metallurgists made as a rule all required efforts in order to obtain close, smooth and laminar outflowing streams. However this is in fact not so easy and very often a sputtering, open and turbulent jet, sometimes called "umbrella jet", is obtained either at the start of the teeming or during the course of the discharge operation. Even if, up to now, the real reasons of the formation of the "umbrella jet" were not exactly known, the metallurgists however knew very well the deleterious metallurgical effects of this phenomenon.
So, in the iron and steel making industry, as well as in the field of the traditional casting into ingot molds, as in the field of the continuous casting, a turbulent stream entraps considerable volumes of air. As a result thereof the metal, in the present case steel, is exposed to an oxidation. The oxidation of the outer skin of the stream results in an increase of the inclusions in the finished product and it is therefore responsible for the negative consequential effect on the degree of the inner purity of the metal, which on the other hand influences the properties of the finished product and its transformality. In the case of the ingot casting the turbulent stream causes moreover in the interior of the ingot mold a foaming and a splashing. The upwardly projected drops of metal solidify untimely along the wall of the ingot mold and are responsible for an insufficient surface quality which leads to rolling defects and faults. If during continuous casting, be it in the case of the outflow of a free or of an unprotected stream, be it in the case of an immersed or of a protected stream, the metal flows in a turbulent manner into the upper part of the mold, it becomes impossible to keep the meniscus more or less constant and motionless. This results in an uncontrolled dragging of slag and in corresponding surface defects on the cast slabs, blooms or billets, as well as in oxide inclusions in the steel.
These uncontrolled occurrences of a turbulent outflow condition have led the metallurgists to take several empiric preventative measures. For example, it have been suggested to use nozzles with a varying ratio "length of the nozzle" to "diameter of the outlet", or to modify the shape and the composition of given parts of the nozzle, especially of the movable parts, or to exchange more frequently the parts of the nozzle subject to wear.
More specifically, Canadian Patent No. 1,200,384 describes a complete sliding closure device for the taphole of a steel shop ladle. This device is characterized by the fact that it comprises a fixed upper part showing a passage of a round cross section and a movable lower part comprising an orifice with a cross section of the shape of an equilateral triangle. The base of the triangle is small and has approximately the same dimension as the diameter of the round passage in the upper device part, whereas the bisector of the triangle coincides with the opening and the closure paths of the device. In view of the closure the lower movable nozzle bearing part of the device is moved in the direction of the apex of the equilateral triangle. This means that, as well in the case of the closure, as in the case of the opening of the device, the terminal part of the jet in the process of being interrupted or respectively the initial part of the jet in the course of being generated are very important. Half-way of the path of the movable lower nozzle bearing part before the passage in the lower fixed part of the device, it is one half of the total outflow section which is uncovered. The vanishing or the nascent streams are directed into the trough gutter which has the same vee-form as the apex of the cross section form of the nozzle. As they flow out those streams give rise to turbulences and to rather important sputtering.